There are many industries in which it is necessary to analyse a liquid sample for the presence of cells, microbes and/or other microorganisms. In particular, quality control in the food and beverage industries commonly requires the analysis of samples of materials such as dairy products, juices, soft drinks, beer, wine and oils for the presence of spoilage organisms, eg microfungi such as yeasts. Regulatory requirements mean that pharmaceutical products and cell cultures are regularly tested for the presence of undesirable microorganisms. Microbiological filtration is also routinely carried out in the testing of potable and waste water, in environmental control and monitoring, in the cosmetics industry, and in the medical field, particularly in diagnostics.
In the medical field, it is often necessary to separate and collect cells from a biological sample in order to enable the cells to be analysed. This may be required, for example, in order to diagnose and/or treat certain diseases. For example, the analysis of cells extracted from a urine sample may be used in the diagnosis of bladder cancer, or the separation of cells from faeces may be used in the diagnosis of cancer of the GI tract.
Conventionally, cells and other microorganisms are collected from fluid samples using a centrifuge, where the forces exerted by a high speed centrifuge cause the larger, denser particles in a sample to sediment out. Typically, the larger particles include cellular material contained within the sample, which has been separated from the fluid component of the sample. Once the cellular material has been obtained, it can be analysed using a microscope or other analytical method.
During the process of centrifugation, the fluid sample and cellular material contained within it are subject to significant forces. These forces can cause damage, such as cell rupture, to the cellular material. This can affect the results which are obtained, and/or may result in it being difficult to reach a conclusion, eg a diagnosis or determination of the microorganisms present, when the extracted material is analysed.
In addition, due to the need for specialist equipment, it is often necessary for the fluid sample to be sent to a remote laboratory in order for centrifugation and analysis to be carried out. This is a particular issue in the analysis of biological samples. Cellular material contained within a biological sample degrades with time, and any time delay between obtaining a sample and analysing it can therefore result in the analysed material becoming damaged. This may affect the results obtained, and/or make it difficult for a conclusion to be reached. The necessity for the use of specialist equipment requiring the sample to be sent to a remote laboratory to be separated and analysed is therefore undesirable, as it introduces delay into the process and so increases the risk of the extracted cells or other microorganisms becoming damaged.
There is thus a need for a method of collecting cells and/or microbiological material from a fluid sample which minimises the damage caused to the collected material, in order to optimise the quality of the extracted cellular and/or microbiological material and so enable accurate determination of the cellular, microbial and/or other microbiological content of the sample to be made.